The present invention relates to vent caps for lead-acid batteries, and more particularly to bayonet-style vent caps.
Many devices use a quarter-turn or bayonet-style attachment in applications where quick installation and removal are desired. For example, lead-acid batteries use this method of attachment for securing the vent caps within the vent ports. The same attachment method is often used in the manufacture of battery watering systems to mount the watering valves to the vent ports.
A typical prior art battery vent cap 10 and vent port are illustrated in FIG. 1. The vent cap 10 includes bayonet tabs 12, and the vent port includes bayonet tabs 24. The tabs 12 and 24 have substantially similar lead angles. The vent cap is tightened within the vent port as the cap is rotated 90° clockwise. This tightening secures the vent cap 10 and provides a seal between the cap flange 14 and the vent port rim 22. The seal prevents the migration of battery acid out of the cell. The vent cap 10 can be easily rotated 90° counterclockwise to remove the cap from the vent port 20 for routine battery maintenance and inspections. The described bayonet attachment system has been used for decades and is still the most common system of attachment for battery vent caps and watering systems on deep-cycle batteries in North America.
Recently, some manufacturers of caps, particularly caps which are part of battery watering systems, have adopted a push-in style of vent cap. An example of this style of vent cap 30 is illustrated in FIG. 3. The cap 30 includes a resiliently flexible circumferential rib 32 which is slightly larger in diameter than the inside diameter of the bayonet tabs 24. This construction enables the cap 30 to be pushed into place with the rib 32 providing a snug fit behind the bayonet tabs 24. This installation method is very fast compared to the normal quarter-turn method. The push-in caps are being used on the assembly line by battery manufacturers and manufacturers of battery-powered equipment, such as golf cart manufacturers. The caps also enable faster installation of battery watering systems in the field. After the caps 30 are pressed into place, the caps can rotate 360° within the vent port, which is helpful in aligning connection ports on the caps with watering system tubing.
The push-in vent caps are not without problems. For example, because (a) the retaining surfaces of the bayonet tabs 24 in the vent port 20 have a lead angle as shown in FIG. 2 and (b) the retaining rib 32 on the cap 30 does not, the retention of the cap is provided by contact in only two diametrically opposite points on the bayonet tabs 24. This two-point contact does not provide a tight seal between the cap 30 and the vent port 20. In fact, the two points of contact form an axis of rotation that enables the cap to rock or tilt, which further reduces the quality of the seal. To combat the tilting effect, the manufacturers of the push-in style caps make the push-in fit very snug and strong to improve the seal and to prevent the cap from popping out of the vent port as the cover flexes during use. The strong fit also assists in maintaining an appropriate seal over a wide range of temperatures and vibrations experienced by the battery. Unfortunately, in order to remove these push-in caps for routine battery maintenance, field personnel use screwdrivers or channel-lock wrenches to pry out or pull out the caps. This methodology has great potential to damage the battery cover and/or cap. It also can be hazardous because it involves the use of a metal tool on the battery top, which can cause dangerous sparks that can trigger explosions. The benefit of rapid installation provided by these push-in caps is therefore offset by the difficult, potentially damaging, and hazardous job of removing the caps for routine battery maintenance.